In recent years, air-conditioned cloths, which ventilate air to evaporate sweat produced by the human body, and heated cloths, which heat the human body by a plate heater, have been put into practice. Detailed description of the principle and structure of an air-conditioned cloth can be found in Patent Document 1 for example.
Portable rechargeable power supply devices using a lithium-ion battery have been used as a power supply of such air-conditioned cloths and heated cloths. Specifically, a portable rechargeable power supply device that is used as the power supply of an air-conditioned cloth for a worker includes a lithium-ion battery and a DC converter for controlling the output power. For example, the lithium-ion battery has a voltage of 7.4 V and a capacity of 4000 mAh, which is composed of four lithium-ion single cells connected in series-parallel each having a voltage of 3.7V and a capacity of 2000 mAh. The DC converter converts the output voltage of the lithium-ion battery to any one of, for example, 4 V, 5 V, 6 V and 7.4V. By using the portable rechargeable power supply device, the user can select a desired voltage according to the working environment.